Fonfara, of Chicago by way of Radon, Poland, dropped Chavez, of Culiacan, Sinaloa, Mexico, with a wide left hook 50 seconds into the ninth round before a boisterous crowd of 8,636 predominately-Chavez fans at StubHub Center. It was the first time in 52 professional fights that Chavez had hit the canvas from a punch.

Upon returning to the corner, Chavez could be heard on the telecast telling trainer Joe Goossen that he had hurt his right leg and could no longer continue. Moments later, the fight was halted. The busier and more accurate fighter throughout, Fonfara was comfortably ahead on the three judges’ scorecards by scored of 89-80 and 88-81 twice after nine full rounds.

Offered an ecstatic Fonfara, who had his fair share of Polish fans at the venue: “I knew he was a tough fighter, quick and in good shape but when he hit me for the first time in the first round, I knew I was going to win this fight. He didn’t punch as hard as everybody said he did.

“I saw his punches easily coming in. I know I threw more punches. I was a little surprised that he did not come out for the (10th) but he was cut, had been getting beat up and had just got knocked down, so he knew what would happen if he came out.

“Chavez said before the fight that he didn’t think I could take his body punches. I think I took them pretty good and passed that test.

“I know there are things I can still work on in training to become a more complete boxer, but tonight was a dream come true. I want a rematch with (Light Heavyweight World Champion) Adonis Stevenson.”

Said Chavez, the son of legendary Mexican icon, Julio Cesar Chavez Sr. in the ring afterward and before he was taken to the hospital as a precautionary measure, “Maybe 170,172 pounds is too big for me, maybe I’ll go back down. I’m not sure what my future holds. It was a very tough fight. But I congratulate Andrzej.”

Goossen told reporters afterward that he had “stopped the fight. It was my decision. I didn’t like what I saw. “

In the first half of a SHOWTIME CHAMPIONSHIP BOXING doubleheader, undefeated world-ranked super lightweight Amir Imam (17-0, 14 KOs), of Davie, Fla., by way of Albany, N.Y., won a lopsided 10-round decision over Walter “The Hammer” Castillo.

The talented, versatile, Imam, 24, controlled a fight that featured numerous exchanges especially early on with a left jab and straight right hand.

“My combinations were effective the whole night, we stuck to our gameplan and came out victorious,’’ said Imam. “I want any of the world champions next’’.

Castillo, who saw a nine-fight winning streak come to an end, said “I thought I won the fight. I didn’t get credit for the punches I threw. The judge who scored it 100-90; well, that gives me no chance to win here. The cut bothered me in the early rounds, but was not a factor after.”

Flores, making his 2015 debut and third start in a row in the United States, triumphed by the scores of 116-112 twice and 113-115.

An emotional Flores was near tears afterward. “This is a dream come true – more than a dream come true – for me,’’ he said. “I saw my family on the beach, eating meat. I saw my babies better dressed. For me this is a life-changing victory and, yes, I thought it was very, very close but I absolutely feel I won.

“I want to fight the best next, the top guys at 122 pounds and right now the top guy is Leo Santa Cruz. That’s who I’d like to fight next. I really want to thank all my team, from top to bottom, for giving me this wonderful opportunity. We’re very happy that we joined the Al Haymon team. We’re very loyal and we just really appreciate everything they’ve done for us.’’

Escandon felt he’d done enough to win despite injuring the right index finger on his right hand in the seventh round.

“I did all that I could, everything was in my reach, but I think I broke or fractured my finger,” he said. “In boxing things happen that are out of your control. Because I hurt my hand, I couldn’t throw punches the way I wanted to with my right hand. I tried to do all I could with it. But I didn’t want to injure it further. I’m OK, but I definitely would love a rematch.’’

Chavez won by the scores of 78-75 twice and 77-74. There were no knockdowns. Unbeaten Argentine welterweight Fabian “TNT” Maidana (6-0, 5 KOs), of Santa Fe, Argentina, the brother of former world champion Marcos Maidana, registered a second-round TKO (32 seconds into the round) over outclassed Cory Vom Baur (2-3), of Vancouver, Wash.

Mauro Ranallo called the SHOWTIME CHAMPIONSHIP BOXING action with Hall of Fame analyst Al Bernstein and former world champion Paulie Malignaggi commentating and Jim Gray reporting. In Spanish, Alejandro Luna called the blow-by-blow with former world champion Raul Marquez serving as color commentator. Barry Tompkins called the SHOWTIME EXTREME action from ringside with boxing historian Steve Farhood serving as expert analyst.

The executive producer of SHOWTIME CHAMPIONSHIP BOXING is David Dinkins Jr. with Bob Dunphy directing.